Harmful ingredients such as heavy metals, acids and powdered glass are used in Holi colors.
The black paste youngsters use has lead oxide, green contains copper sulphate, and red has mercury sulphite and so on. All these are toxic and can result in skin allergies.
Many dry powders use a base of asbestos talc, chalk powder or silica. Silica may dry as well as chap the skin. The shine in the colours is due to the addition of powdered glass or mica. Synthetic colours often contain lead oxide, engine oil, diesel, chromium, iodine and copper sulphate, which cause skin irritation in case of extreme exposure.
It's suggested that one should only buy skin-friendly natural colours. But where to get these natural colors...